This invention is related to the type of low-lifting fork trucks that are used to move loading pallets with load in the floor plane. These types of trucks are for instance used for the transferring of loads from lorries into supermarkets or the like and in particular for reloading of freighted goods to and from or between different long distance lorries. In particular the latter use is increasing since the aim is to store the merchandise for as short a time as possible between the producer and buyer, and instead a swift continuous flow from maker or producer to the final buyer or user is desired. The desired swiftness in the reloading thus not only leads to an increased use of these types of trucks but also to an increased demand on their speed. The speeds are already today such that in some cases safety belts are required for the drivers, this in order to avoid injuries at collisions etcetera, as well as to avoid that the driver falls off. The increased speed further means that damage to the transported goods increases, maintenance costs of the trucks increase and the drivers are subjected to harmful vibrations.
The increased speeds do not only mean increased damage at collisions but also mean that an uneven surface of the floor, that at traditional speed are not noted at all, are transformed into shocks that in the long run may become disturbing and tiresome for the driver. These shocks may also lead to the transported goods xe2x80x9cshaking or bouncingxe2x80x9d off from the loading pallet. Since the support wheels of the truck bounce on the floor a reduction in traction results that in some instances may make the truck more difficult to steer. Trucks that are used today lack a separate spring system. The only damping component is the coating of the wheels. With the increasing demand on speed one has to reduce the xe2x80x9cdampingxe2x80x9d coating of the wheels since a high damping and a high speed will result in a too high heat generation for the wheels. This means that there is a trend towards a situation where damage of trucks, goods and drivers will increase since the dynamic strains increase with speed, and at the same time future demands of even larger loads can be expected to make the problem even worse.
The object of the invention is to eliminate or at least reduce these problems. In accordance with the invention the above problems are solved by providing the fork truck with a spring system (in addition to that, that may possibly exist in the coating of the wheels).
In general these types of trucks have small support wheels or rollers arranged in the front ends of the forks, which wheels due to their small diameter are particularly sensitive to un-evenness in the floor. It is therefor particularly desirable to provide these wheels with a spring system and one can therefor possibly be satisfied with providing only these wheels with a spring system.
For one skilled in the art of trucks a spring arrangement for the wheels is not logical since the truck at a possible off centered load preferably is not to become inclined since it then may more easily lose its cargo or become unstable. Since furthermore the load of a truck can vary by several tons the spring movement will as is realized either be too long or the springing too hard, in particular when the truck is to be driven empty or with only a small load. In accordance with a further development of the invention this problem is however solved by making the spring system load dependent, for instance by a pretensioning of the working spring device that is proportional to the weight of the load. When a small rock or other protruding unevenness is hit by a spring suspended truck wheel the pretension is overcome by the temporary dynamic additional load and the wheel springs up and reduces in this way the shock that is a result of the unevenness.